A modified method for removal and stabilization of cesium metal in vitrified matrix
Laboratory experiments were designed to investigate the separation and stabilization of cesium metal. Cesium was removed from simulated waste through sorption under certain physicochemical conditions. Silica sand (locally purchased) was used to remove cesium from simulated liquid waste. The range of...
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Інститут колоїдної хімії та хімії води ім. А.В. Думанського НАН України
2012
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| Цитувати: | A modified method for removal and stabilization of cesium metal in vitrified matrix / Ghaffar Abdul, Mazhar Farhana, Mashiatullah Azhar, Abdulaziz S. Alaamer // Химия и технология воды. — 2012. — Т. 34, № 6. — С. 440-449. — Бібліогр.: 22 назв. — англ. |
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irk-123456789-1307322018-02-21T03:03:04Z A modified method for removal and stabilization of cesium metal in vitrified matrix Ghaffar Abdul Mazhar Farhana Mashiatullah Azhar Abdulaziz S. Alaamer Физическая химия процессов обработки воды Laboratory experiments were designed to investigate the separation and stabilization of cesium metal. Cesium was removed from simulated waste through sorption under certain physicochemical conditions. Silica sand (locally purchased) was used to remove cesium from simulated liquid waste. The range of pH and temperature was optimized and maximum removal (94 – 98 %) of cesium was achieved with pH 10 at temperature 36°C. Under optimized conditions with temperature range of 301– 315K ΔH, ΔS and ΔG309K for 150 ppm solution are – 27.22±0.18 KJ/mol, – 74.1± 0.96 J/mol and – 3071±2.1 KJ/mol respectively, and for 200 ppm solution thermodynamic entities are ΔH= – 20.2±0.20 KJ/mol, ΔS = – 47.86±0.66 J/mol and G301K = – 4344±3.7 KJ/mol. The sorbed metal ion has chances of desorption under changed physicochemical conditions in final disposal. To overcome this problem the final "secondary waste (metals on sorbents)" was stabilized by converting it into a stable vitreous borosilicate matrix through vitrification process to prevent leaching. It was found that the sorbed cesium was evaporated during heating at 1250°C. The evaporation of cesium during vitrification was overcome by modifying the process. This modified vitrification process is found excellent to immobilize the sorbed cesium. Stability was tested by desorption attempts at different pH. 2012 Article A modified method for removal and stabilization of cesium metal in vitrified matrix / Ghaffar Abdul, Mazhar Farhana, Mashiatullah Azhar, Abdulaziz S. Alaamer // Химия и технология воды. — 2012. — Т. 34, № 6. — С. 440-449. — Бібліогр.: 22 назв. — англ. 0204-3556 http://dspace.nbuv.gov.ua/handle/123456789/130732 en Химия и технология воды Інститут колоїдної хімії та хімії води ім. А.В. Думанського НАН України |
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Физическая химия процессов обработки воды Физическая химия процессов обработки воды |
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Физическая химия процессов обработки воды Физическая химия процессов обработки воды Ghaffar Abdul Mazhar Farhana Mashiatullah Azhar Abdulaziz S. Alaamer A modified method for removal and stabilization of cesium metal in vitrified matrix Химия и технология воды |
| description |
Laboratory experiments were designed to investigate the separation and stabilization of cesium metal. Cesium was removed from simulated waste through sorption under certain physicochemical conditions. Silica sand (locally purchased) was used to remove cesium from simulated liquid waste. The range of pH and temperature was optimized and maximum removal (94 – 98 %) of cesium was achieved with pH 10 at temperature 36°C. Under optimized conditions with temperature range of 301– 315K ΔH, ΔS and ΔG309K for 150 ppm solution are – 27.22±0.18 KJ/mol, – 74.1± 0.96 J/mol and – 3071±2.1 KJ/mol respectively, and for 200 ppm solution thermodynamic entities are ΔH= – 20.2±0.20 KJ/mol, ΔS = – 47.86±0.66 J/mol and G301K = – 4344±3.7 KJ/mol. The sorbed metal ion has chances of desorption under changed physicochemical conditions in final disposal. To overcome this problem the final "secondary waste (metals on sorbents)" was stabilized by converting it into a stable vitreous borosilicate matrix through vitrification process to prevent leaching. It was found that the sorbed cesium was evaporated during heating at 1250°C. The evaporation of cesium during vitrification was overcome by modifying the process. This modified vitrification process is found excellent to immobilize the sorbed cesium. Stability was tested by desorption attempts at different pH. |
| format |
Article |
| author |
Ghaffar Abdul Mazhar Farhana Mashiatullah Azhar Abdulaziz S. Alaamer |
| author_facet |
Ghaffar Abdul Mazhar Farhana Mashiatullah Azhar Abdulaziz S. Alaamer |
| author_sort |
Ghaffar Abdul |
| title |
A modified method for removal and stabilization of cesium metal in vitrified matrix |
| title_short |
A modified method for removal and stabilization of cesium metal in vitrified matrix |
| title_full |
A modified method for removal and stabilization of cesium metal in vitrified matrix |
| title_fullStr |
A modified method for removal and stabilization of cesium metal in vitrified matrix |
| title_full_unstemmed |
A modified method for removal and stabilization of cesium metal in vitrified matrix |
| title_sort |
modified method for removal and stabilization of cesium metal in vitrified matrix |
| publisher |
Інститут колоїдної хімії та хімії води ім. А.В. Думанського НАН України |
| publishDate |
2012 |
| topic_facet |
Физическая химия процессов обработки воды |
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http://dspace.nbuv.gov.ua/handle/123456789/130732 |
| citation_txt |
A modified method for removal and stabilization of cesium metal in vitrified matrix / Ghaffar Abdul, Mazhar Farhana, Mashiatullah Azhar, Abdulaziz S. Alaamer // Химия и технология воды. — 2012. — Т. 34, № 6. — С. 440-449. — Бібліогр.: 22 назв. — англ. |
| series |
Химия и технология воды |
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| fulltext |
440 ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6
ABDUL GHAFFAR, FARHANA MAZHAR, AZHAR MASHIATULLAH, 2012
A MODIFIED METHOD FOR REMOVAL AND
STABILIZATION OF CESIUM METAL IN VITRIFIED
MATRIX
Abdul Ghaffar1, Farhana Mazhar2, Azhar Mashiatullah1,
Abdulaziz S. Alaamer3
1IAD, PINSTECH, P.O. Nilore, Islamabad, Pakistan;
2Department of Chemistry Lahore College for Women University, Lahore,
Pakistan;
3Al-Imam Muhammad Ibn Saud Islamic University, Riyadh, Saudi Arabia
Received 07.06.2011
Laboratory experiments were designed to investigate the separation and stabilization
of cesium metal. Cesium was removed from simulated waste through sorption under
certain physicochemical conditions. Silica sand (locally purchased) was used to
remove cesium from simulated liquid waste. The range of pH and temperature was
optimized and maximum removal (94 – 98 %) of cesium was achieved with pH 10
at temperature 36°C. Under optimized conditions with temperature range of 301–
315K H, S and G
309K
for 150 ppm solution are – 27.22±0.18 KJ/mol, – 74.1±
0.96 J/mol and – 3071±2.1 KJ/mol respectively, and for 200 ppm solution
thermodynamic entities are H= – 20.2±0.20 KJ/mol, S = – 47.86±0.66 J/mol and
G
301K
= – 4344±3.7 KJ/mol. The sorbed metal ion has chances of desorption under
changed physicochemical conditions in final disposal. To overcome this problem the
final "secondary waste (metals on sorbents)" was stabilized by converting it into a
stable vitreous borosilicate matrix through vitrification process to prevent leaching.
It was found that the sorbed cesium was evaporated during heating at 1250°C. The
evaporation of cesium during vitrification was overcome by modifying the process.
This modified vitrification process is found excellent to immobilize the sorbed cesium.
Stability was tested by desorption attempts at different pH.
Keywords: cesium removal, borosilicate matrix, leachibility physiochemical
conditions, sorption and kinetics, stabilization.
Introduction
Cesium is used in industry as a catalyst promoter, boosting the performance
of other metal oxides in the capacity and for the hydrogenation of organic
compounds. Cesium occurs naturally in the environment mainly from erosion
and weathering of rocks and minerals. Cesium salts are used to strength various
types of glass. Cesium nitrate is used to make optical glasses. Cesium is
sometimes used to remove traces of oxygen from the vacuum tubes and from
light bulbs. The chloride is used in photoelectric cells, in optical instruments,
and in increasing the sensitivity of electron tubes. Cesium is used in atomic
ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6 441
clocks and more recently in ion propulsion systems. It is released into the air,
water and soil through industrial effluents, mining and milling of ores. In water
and soils most cesium compounds are very water-soluble. It remains within
the top layers of soils as it strongly bonds to soil and silica particles and as a
result it is not readily available for uptake through plant roots. Cesium in air
can travel long distances before settling on earth. In soils, however, cesium
does not rinse out into the groundwater.
Humans may be exposed to cesium by breathing, drinking or eating. Due
to this, effects such as nausea, vomiting, diarrhoea and bleeding may occur.
When the exposure lasts a long time people may even lose consciousness.
Coma or even death may than follow. How serious the effects are depends
upon the resistance of individual persons and the concentration a person is
taken to [1]. Cesium is not biodegradable like other toxic pollutants and once
in the environment, their potential toxicity is controlled by their physiochemical
form [2, 3]. Soils [4 – 7] and clays [8 –11] with aluminosilicates are found to be
very selective ion exchangers for many cations and exhibit very high stability,
many clays exhibit excellent sorption activity with Montmorillonite as a major
constituent. Both the natural and synthetic Zeolites have also been reported
for the sorption of cesium [12 – 14]. The removal is maximized under certain
physiochemical conditions therefore there are chances of the desertion of the
adsorbed metal ions under changed physiochemical conditions in final disposal.
This possibility emphasized the need to stabilize these adsorbed metals ions
after sorption. Solidification/stabilization (S/S) reduces the mobility of
hazardous substances and contaminants in the environment through both
physical and chemical means. Unlike other remedial technologies, S/S seeks
to trap or immobilize contaminants within their "host" medium i.e., sand, that
sorbed them).
Due to the large amount of glass network former in sand, it is cheap and a
promising basic material for glass. Because of its good chemical durability
and inexpensiveness, S
i
O
2
is the most widely used glass forming oxides and
therefore the major ingredients of glass. Many glass forms of different waste
streams have been developed [15, 16]. The chemical resistance of glass can
allow it to remain in a corrosive environment for thousands or millions of
years. Other strong reason is that glass has an ability to incorporate the waste
contaminates in its microstructures [17]. The silica sand contains 80.361 %
S
i
O
2,
was chosen for adsorption provided a basis from which glass formulation
was developed. The cesium metal was sorbed onto the silica sand and then
developed into glass frit with required characteristics regarding to its stability.
The development of suitable glass without considerable addition of further
additives with reasonable melting temperature is an achievement of present
work. During vitrification process cesium has tendency to evaporate at
temperature above 600°C which was overcome by modifying the vitrification
442 ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6
process. This modified vitrification process is found excellent to immobilize
the sorbed cesium. Leachability testing is typically performed to measure the
immobilization of contaminants at different pH and temperature.
Experimental
Silica sand (Locally purchased) was washed twice with distilled water
after washing with dilute HCl and dried in air. The composition of silica sand
(Table 1) was analyzed by inductively couple plasma spectrometry (ICP) and
X-ray diffractions technique. An assembly of glass columns was used for the
sorption treatment with dimensions of,inner diameter 2.3 cm, bed height
15.7 cm, volume 68 cm3. The weight of the silica sandfilled in column was
18.64 g. For sorption treatment the effluents were allowed to pass through the
glass columns packed with silica sand. The removal efficiency of adsorbent
was maximized by varying pH of samples and temperature.
Table 1. Chemical composition of silica sand (oxide basis, Wt, %)
Oxides Wt, %
SiO2 80.361
Al2O3 5.301
CaO 4.369
Fe2O3 2.988
MgO 1.456
Na2O 1.232
K2O 1.101
MnO 0.053
ZnO 0.004
Silica sand was carefully introduced from the top, continuous tapping
ensured the uniform packing up to desired level. The known volume of 150
and 200 ppm solution of cesium (prepared from cesium nitrate) were run
through the column packed with sorbent.
The effluent was collected from the bottom in plastic bottles and again
analyzed for the concentration of cesium. The change in the concentration of
cesium after treatment was calculated by taking difference between two
ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6 443
concentrations. The concentration of cesium ions in solutions was measured
by atomic absorption spectrophotometer (Hitachi Z-2000) equipped with hollow
cathode lamp of cesium. The percentage sorption (R, %) and distribution
coefficient (K
d
) was calculated using following relationship:
R =
t
ti
C
CC
100;
m
V
C
CC
K
t
ti
d
,
where C
i
is the initial concentration (ppm) of the cesium in solution and C
t
concentration of solution after treatment, V = volume of sorbate (cm3) and m =
amount of sorbent (g).
Results and Discussion
Table 2 showed the effect of pH of sample on sorption, three different
samples were prepared with different pH values which were as, 2, 4, 7, 10 and
12 using buffer solutions of acetic acid/sodium acetate and ammonium
hydroxide/ammonium chloride, respectively. The removal of cesium by sorbents
was highly dependent on the pH of the solution which affects the surface charge
of the sorbents, degree of ionization and speciation of the sorbates. Samples
with different pH were passed through columns filled with silica sand. The
change in sorption efficiency with change in pH of samples was found to be
significant. The maximum sorption was obtained at pH 10 [18], as shown in
Fig.1. The difference in removal efficiency due to the solution pH was attributed
to the precipitation of cesium hydroxide at a higher pH. Increasing the pH
implied a promotional increase of OH ions concentrations in solution disturbing
equilibrium which could be achieved again through formations of greater
amount of hydroxide out of the solution.
Table 2. Effect of pH on the removal of Cs
Removal (%) at pH Adsorbing material
(packed in 2.3 cm
15.7cm column)
Conc. of
Cs (ppm)
2 4 7 10 12
150 62 68 85.5 9 82
Silica Sand
200 64 66 87 9 82.
444 ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6
Table 3 explained the effect of temperature on sorption. Each sample
solution with different temperature i.e. 25°C, 28°C, 32°C, 36°C, 40°C and
42°C was passed through the sorbents. It was observed that the sorption of
cesium was increased with the increase in temperature as reported by [19, 20],
and maximum sorption was achieved at 36°C. The sorption was then decreased
as the temperature was increased more than 36°C with order as: 42°C < 40°C
< 36°C > 32°C > 28°C >25°C.
R
em
ov
al
(
%
)
0 2 4 6 8 10 12
50
70
90
pH
150 ppm
200 ppm
Fig. 1. Removal of Cs at different pH.
Table 3. Effect of temperature on removal of Cs
Removal (%) at temperature Adsorbing material
(packed in 2.3cm
15.7cm column)
Conc. of
Cs (ppm) 25°C 28°C 32°C 36°C 40°C 42°C
150 80 89 90 94 77 70
Silica Sand
200 82 90 93 98 80 72
The values H, S were calculated from the slope and intercept of the
l inear Van’ t Hoff plot of log K
c
Vs 1/T where K
c
= F/1 – F and T is absolute
temperature in Kelvin and F represents the fraction sorbed at equilibrium.
The values of H and S were computed using the relations:
logK
c
= – H/2.303RT + S/2.303R.
The free energy of adsorption G was calculated using equation
G = – RT ln K
c
.
ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6 445
The slope and intercept of Fig.2 gave thermodynamic entities for 150 ppm
and 200 ppm solution. The values of thermodynamic entities are given in
Table 4. The negative enthalpy and negative free energy reflect the exothermic
and spontaneous nature of sorption respectively.
1.2
0.8
log Kca
0.4
0
3.36 3.34 3.32 3.30 3.28 3.26 3.24 3.22
103/T
1.6
1.2
log Kc
b
0.8
0.4
0
3.40 3.35 3.30 3.25 3.20
103/T
Fig. 2. Removal of Cesium 150 ppm (a) and 200 ppm (b) at different temperature
at pH 10.
Table 4. Thermodynamic quantities for sorption of Cs
Thermodynamic quantities Adsorbing material
(packed in 2.3cm ×
15.7 cm column)
Conc. of Cs
(ppm)
H,
KJ/mole
S,
J/mole.K
G,
KJ/mole
150 – 27.22±0.18 – 74.1±0.96 – 3031±2.1
Silica Sand 200 – 20.2±0.20 – 47.86±0.66 – 4288±3.7
446 ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6
The results of cesium concentration dependence study on sorbents were
also subjected to analysis in terms of Langmuir and Freundlich adsorption
isotherms. The data do not fit for Langmuir equation. However Freundlich
adsorption isotherm was capable of describing the data over the concentration
range studied. The Freundlich isotherm was tested in the following linearized
form:
log C
ads
= log A + 1/n log C
e
,
where C
ads
– amount of cesium ion adsorbed at equilibrium (mol/g); C
e
–
equi l ibrium concentration of cesium in the solution (mol/dm3); A and 1/n –
Freundlich constant.
Almost all this adsorptive separation processes depend on physical sorption
rather than chemisorptions and this therefore the focus of the present review.
The heat of sorption provides a direct measure of the strength of the bonding
between sorbate and surface. Physical sorption from the liquid phase is
invariably exothermic, although there are very small heat changes, as may be
shown by a simple thermodynamic argument. Since the sorbed molecule has
at most two degrees of translational freedom on the surface and since the
rotational freedom of the adsorbed species must always be less than that of the
liquid phase molecule, the entropy change on sorption S = S
ads
– S
gas
is
necessarily negative. In order for significant sorption to occur, the free energy
change on sorption G must also be negative and since G = H – TS, this
requires H negative, or exothermic sorption. Therefore maximum sorption at
temperature (36°C) and low sorption at higher temperature is exactly according
to this theory.
Once the cesium has removed from the industrial effluent through sorption
then the next step is its stabilization which was achieved by converting the
sorbent into the stable and leach resistant glass matrix.
There has much research focused on the composition durability relationship
of glass. The glass formers are the major constituents of all waste glasses. If
the inorganic oxides present in the silica sand have insufficient glass formers
to fall within the accepted formulation range, additional glass formers must be
added through the process. The silica sand selected for sorption has suitable
composition required to develop a glass frits. The attempt was made to develop
different glass formulations by varying composition of modifiers and fluxes
based on the calculations. The developed glass frits were characterized mainly
focusing on their density and leachibility.
Density was measured on basis of volume displacement method using
simple relation of D = m/v, where m is mass of glass and v is the volume
displaced by sample when dipped in known volume of water.
ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6 447
In order to rapidly determine the chemical durability of the glass, a leaching
test method was derived from the standard PCT leach test method named as
M-PCT. The glass sample grinded and attain in the particle size of 1.0 – 1.2 mm.
the sample was washed with the acetone to remove the fine particles before
testing. The surface area of the sample was calculated by following equation
[21, 22]:
SA = 6M / Ø . 0.89,
where SA is the surface area in cm2, M the mass (g) of the glass sample, is
density (g/cm3) of glass sample, Ø is average diameter in cm and 0.89 is
factor to convert the results from sphere particles to glass.
The sample was first leached for 19 hours in an ammonium hydroxide
buffer of pH 9, followed by a second leach of 19 hours in an acetate buffer of
pH 3.9, both solutions at ambient temperature. After exposure to the buffered
solutions, the glass was leached for 24 hours at 99°C in deionized water. The
leachate of every phase was analyzed using Inductively Coupled Plasma
spectrometry (ICP) for the concentration of Si, Na, Al and particularly Cs. The
total mass loss of glass (ML) and the normalized elemental loss (NL) were
obtained. The ML and NL were used to monitor the chemical durability of
glass forms during glass formulations development. The ML value was
calculated as follows:
ML = (m
o
– m
1
) SA,
where ML is total mass (gm) lost, m
o
the mass (gm) of unleached specimen,
m
1
the mass (gm) of specimen after leaching and SA is the sample surface area
(m2). Regarding to elemental analysis in leachate, the normalized element mass
loss NL was calculated using formula:
NL = C
i
. V . SA . f
i
,
where NL is element mass (g/m2) lost, C
i
is the concentration of element (g/m3)
in the leachate, V is the volume of leachant (m3), f
i
is the mass fraction of
element in unleached glass sample.
Amongst the studied formulations the composition, AG 327 was found
excellent in terms of its low leachibility and greater chemical stability. The
formulation AG 327 contains 10 % Na
2
O where as the percentage of Na
2
O in
studied silica sand was only 1.2 %. This difference in percentage of Na
2
O
from 1.2 % to 10 % was achieved by adding 15.04 gm Na
2
CO
3
as source
material calculated by the given formula as:
448 ISSN 0204–3556. Химия и технология воды, 2012, т. 34, №6
Wsm = Wpm .100/Cpm,
where the Wsm is weight (gm) of the source material, Wpm is the required
weight (gm) of particular metal oxide and Cpm is contents of particular metal
oxide in used source material. The Na
2
CO
3
was used as the source material for
its alkali metal oxide (Na
2
CO
3
gives 58.5 % Na
2
O on thermal decomposition ).
The silica with sorbed cesium was converted to the composition (SG) and
was heated at 1250°C. During melting process the fumes were collected in the
cold water. The water was analyzed and cesium traces were found in the water.
It indicated that during heating of the matrix at temperature 1250°C, cesium
was evaporated. To overcome this problem, the silica along with the sorbed
cesium was first mixed with calculated amount of Na
2
CO
3
(15.04 g) and was
heated at 500°C and cooled. The vitreous material obtained in this result was
converted into a composition (SG) and was melted at 1250°C. The fumes during
melting were collected in the cold water. The water was analyzed for cesium
traces and there was no cesium found in the water. The end product has excellent
glass appearance without bubbles and any crack.
Conclusion
Silica sand, a cheaper and abundantly available material, was proved to be
an excellent sorbent for sorption of cesium from aqueous solutions under certain
physiochemical parameters. The maximum sorption can be obtained at 36°C
in basic media (pH 10). The negative value of H and negative value of G
show the exothermic and spontaneous nature of sorption respectively. The
maximum sorption at 36°C supports the exothermic nature of sorption. The
lower sorption at higher acidic concentration and lower pH values may be due
to the competition between the positively charged cesium and H+. The lower
sorption at higher pH might be due to the surface complexation phenomenon,
which is facilitated by the dissociation of surface functional groups. The silica
sand was proved a best glass forming material as it contains almost all basic
component required to develop a good quality glass. The composition of the
silica sand was modified to suitable composition by adding small amount of
Na
2
O. To overcome the evaporation of cesium during heating, silica having
sorbed cesium was first mixed with the calculated amount of Na
2
CO
3
and
heated at 500°C and cooled to room temperature. Later on, this vitrous material
was converted into the composition (SG) and was melted at 1250°C and the
glass matrix was achieved. The leachibility test was performed in both acidic
and basic media which was ignorable. A comparative experimental data
obtained in this study reveals that silica sand may be employed for the removal
and stabilization of cesium from aqueous industrial effluents before discharging
them into water bodies. As the silica sand is a good sorbent for other heavy
metals also therefore this technique may be applied for removal and stability
of other heavy metal ions as well.
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